In a successive approximation type A/D conversion device (SARADC: Successive Approximation Routine Analog-to-Digital Converter) using a capacitive D/A converter (capacitive DAC), A/D conversion is performed by using a plurality of capacitors, switches that switch a connection relation of the capacitors and a comparator. Each of the plurality of capacitors in the SARADC has a binary-weighted capacitance value, and to each of the capacitors, a reference voltage source, a ground and the like are connected via a changeover switch. Specifically, A/D conversion is realized by redistributing charge accumulated in each of the plurality of capacitors.
As an application of the SARADC, there has been proposed a pipelined SARADC in which combinations of a plurality of SARADCs and basic arithmetic circuits are connected in cascade and in multistage, and are operated in a pipeline manner.
In the SARADC that requires basic calculation processing, there is a need to make a settling error of a reference voltage to be close to zero as much as possible for reducing a calculation error. The settling error depends on a settling time of a reference voltage driving circuit, and for reducing the settling time, a large drive current was required. This requires an amplifier that supplies the large drive current, and thus was a cause of enlarging a circuit scale. Further, this was also a part of the reason of increasing power consumption.
Embodiments described herein were made to solve such problems, and an object thereof is to provide an A/D conversion device and a radio device capable of reducing power consumption and reducing a circuit scale.
In order to achieve the above-described object, an A/D conversion device according to one aspect of the embodiments includes: a D/A conversion unit sampling an analog input signal, generating a comparison signal for successive comparison with the analog input signal by using a reference signal, and generating a difference signal between the analog input signal and the comparison signal; a precharge capacitor unit holding the reference signal; a comparing unit comparing the comparison signal with a reference value to generate a digital signal; and an amplifying unit calculating by using the difference signal and the reference signal to generate a residual signal.
According to the embodiments, it is possible to reduce power consumption and to reduce a circuit scale of an A/D conversion device and a radio device.